Embodiments of this invention relate generally to drilling. More specifically, but not by way of limitation, systems and methods are described for controlling and/or harnessing the vibration of various portions of a drill bit, as well as for directionally drilling cavities drilled in/through earthen formations.
Drill bits used for drilling in earthen formations, as well as other mediums, often have cutters on the head of the drill bit and ridges on the sides of the drill bit. The ridges on the side of the bits are often referred to as gauge pads, and may serve to confine or direct the cutters on the head of the drill bit to a continued path through the medium related to the path already taken by the cutters on the head. In some drill bits, cutters may be placed on all or a portion of the gauge pads.
Interactions between the gauge pads and the bore wall of the cavity, which are not intended to be as significant as the interaction of the cutters on the head of the drill bit with the cutting face of the borehole can cause backward whirl. Backward whirl may cause damage to cutters both close to the center of the bit, as well as cutters outward from the center.
Energy wasted by the reaction of the gauge pads with the borehole wall of the cavity may be wasteful in at least two respects. First, any energy wasted by damaging the cutters on the drill bit head is energy which is not being applied to maximize drilling force, and hence speed, through the medium. Second, damage to the cutters on the drill bit head eventually requires the drill bit to be replaced, reducing speed and increasing cost of drilling.
The prior art is therefore deficient in providing a system for avoiding these harmful forces and/or causing them to only occur in favorably lateral directions when steering a drill bit during directional drilling. Embodiments of the present invention provide solutions to these and other problems.